Interannual variability of the sea surface ... - Wiley Online Library

19 downloads 108 Views 561KB Size Report
Jul 15, 1999 - river runoff (there is no major river in the region, as seen in Fig. 1, and the drifter ... low-salinity tongue reaches much lower latitudes than dur-.
GEOPHYSICAL RESEARCH LETTERS, VOL. 26, NO. 14, PAGES 2061-2064, JULY 15, 1999

Interannual variability of the sea surface temperature in the South Brazil Bight Edmo J. D. Campos Instituto Oceanogrgfico,Universidade de S&o Paulo, Brazil

Carlos A.D.

Lentini

RSMAS, University of Miami, Miami, FL

Jerry L. Miller Naval Research Laboratory, Stennis Space Center, MS

Alberto

R. Piola

Depto. de Oceanografia,Serviciode Hidrografia Naval, and Depto. de Cienciasde la Atmosfera, FCEN, Univ. de Buenos Aires, Argentina

expected mass of cold and fresh water was observed on the

In a study basedon historical hydrographicdata along the easternSouthAmericanContinentalShelf [Piota et at., 1999]suggestthat the low-temperature,low-salinitywater

continentalshelfnear 23øS.Subsequent analysesof different

mass could result

data setssuggestedthat the origin of that water was probably the Argentine continental shelf, near the Rio de la Plata mouth. In this article, a 13-year time seriesof AVHRR Sea Surface Temperature anomaliesis analyzed to investigate the occurrence of this phenomenon in other periods. The results of these analyses and a good correlation with the Southern Oscillation Index suggestthat the penetration of these waters into the SBB occurs in a frequencythat may

salinityplumeformedby the Rio de la Plata (-• 35øS)and the Patos/Mirim Lagooncomplex(32øS)outflows.The cli-

be associated

a departure from the normal seasonalvariation. Two recent works on the arrival of cold water biota in a tropical lati-

Abstract. In the austral winter of 1993, during a COROAS

hydrographiccruisein the SouthBrazil Bight (SBB), an un-

with

ENSO

events.

from the northward

extension

of the low

matological distribution of surface salinity on the continen-

tal shelfis dominatedby a strongseasonalvariation [Piota et at., 1999]. In wintertime, the nortward extensionof the

low-salinity tonguereachesmuchlowerlatitudesthan during the summer. However, what was observedduring the

winter of 1993(or in the winter of 1983) can be regardedas

tudesaslow as 22øS [Stevenson et at., 1998; Tommasiet at., 1999],and anecdotalevidences,suchas aperiodicreportsof

1. Introduction Analysis of hydrographic, drifter and satellite data col-

lected in the South Brazil Bight (SBB) during the austral Winterof 1993,revealedthe presence of a massof relatively

penguinson the beachesof Rio de Janeiro during somebut not every winter, leads one to believe that this phenomenon should be classified as a non-seasonal

feature.

cold(•447ø C) andlowsalinity(33.0-34.0) waterbetween the coastand the Brazil Current (Fig. 1) [Camposet at., 1996a]. As suggestedby AVHRR sea surfacetemperature (SST) imagesandby satellitetrackeddrifters[Camposet at.,

2. The data and methodology The data used in this work were satellite-derived

1996b], theobserved low-temperature watermassextdndedtimates,

SST es-

provided by the U.S. National Oceanic and Atmo-

sphericAdministration/National EnvironmentalData Service (NOAA/NESDIS). These SST estimatesare derived velocity,estimatedfrom the drifter data, was 10.7 cm s-x from Global Area Coverage(GAC) data collectedby the [Campos et al., 1996a,b]. Theabsence of anymajgrriver AdvancedVery High ResolutionRadiometer(AVHRR) onin the SBB region and the analysisof satellite and drifter boardpolar-orbitingsatellitesof the NOAA-N series(NOAAdata setsruled out the origin of this water being from local 7 to NOAA-13, in the presentcase). The SST time series river runoff (there is no major river in the region,as seen analyzed here span 13 yearsfrom January 1982 to December in Fig. 1, and the drifter tracksin Camposet al. [1996a] 1994. For studying the inter-annual variability, the methodolclearlyidicatea northwardflowfrom souhternlatitudes). A similar event was observedin a satellite SST image of June ogy describedby Podestaet al. [1991]was usedto remove 17, 1983 (NOAA-7), processedat the Universityof Rhode the seasonal component of the SST time series. The time history of the resultinganomaliesalong the South American Island [Lino and Mascarenhas, 1985].

fromthe vicinityof the Rio de La Plata estuary(35ø3S), to ß

latitudes as low as 23ø S. The typical averagenorthbound

Continental shelf, from 42øS to 22øS, were then presented

as time sequences of residualsversuslatitude (Hovm511er di-

Copyright1999 by the AmericanGeophysicalUnion.

agrams).Resultsfroma mid-shelftransect(alongthe 100m isobath)areshownin Fig. 2. The SST anomalies(SSTA) at a point locatedin the SBB (26ø 15'S, 47ø43'W), is plotted

Papernumber1999GL900297. 0094-8276/99/1999GL900297505.00

2061

2062

CAMPOS ET AL.- SST VARIABILITY

IN THE SOUTH BRAZIL BIGHT

(øC) - 3.0 - 2.5

.... ßI 2.0 1.5 WOCE/½OROi•S/INPœ/BSH

0.5 0.0 -0.5 -1.0

•:1.0

A•HRR/NOA•-11

-1.5

-2.0 -2.5 -3.0

07-20-93

17

1982

1983

1984

1984

1985

1986

r Figure

1. AVHRR derived SST. The blue colorsrepre-

sent low temperature water coming from the southwest into the area surveyed during the COROAS Cruise, during the austral

winter

of 1993.

of the normal

northernmost

limit

)"--' )ß

,: õ'3øI• : ..... '•-32-' "

•--o, - (øC)

k•j Ji.